1. Field of the Invention
This invention is directed to the field of displays, and, more particularly, to an interlocking plastic display using a submerged grid system to reduce the overall thickness of the display.
2. Background of the Prior Art
Many different types of display devices are in common use, such as, for example, name tags, outdoor signage, advertising displays, and markings for utility poles and underground cables. Despite the different applications and uses, purchasers of such devices have some common criteria for deciding what type of display to purchase, and chief among them is the price of the display. In some applications where the display is used in harsh conditions (such as outdoor advertising, or in tagging underground cables) or is worn on a daily basis, durability is a key concern.
With these concerns in mind, U.S. Pat. No. 4,835,890 (the disclosure of which is hereby incorporated by reference) discloses an interlocking plastic display in which a first plastic member is injection molded in the shape of a desired display, in a first injection shot. A second plastic member of a contrasting color is then formed about the first member, also by injection molding, so that the two members mate and interlock to form a rugged display usable in even the harshest environments. In this display, the first member of the interlocking plastic display is a display member having an upper indicia portion and a lower locking portion. The lower portion of the first member comprises a series of open grooves or apertures extending along the width of the display. The indicia portion sits atop the universal lower locking portion, and is joined thereto. The grooves of the lower locking portion are formed with a stepped cross section, so that the second, background, member of the display may be formed around and in the grooves, thereby permitting the two members to interlock.
This display has worked well, generally, but after some experience with manufacture and production of such displays, some problems were observed. Under certain conditions, the display sometimes warped during use along the lines forced by the open grooves, especially in larger signs, which necessitated additional production costs to rectify. On occasion during manufacture, there was an uneven flow of material in the two-shot injection process.
An improved interlocking plastic display is disclosed in U.S. Pat. No. 5,265,364 (the disclosure of which is also incorporated by reference). In this improved display, the display is made of a three-layered display member: an upper indicia layer, a middle universal grid and a lower spacing layer. The concept was that the spacing layer would have a reduced overall volume of material compared to the middle grid layer. The large amount of open volume beneath the grid layer, between the individual spacers in the spacer layer would facilitate the flow of the second shot background material around the first shot display portion, since the middle universal grid would allow the material forming the background portion to flow more evenly through the entirety of the display. Since the lower spacer portion had a smaller overall profile, the background material would be able more easily to flow above and below the grid to permit the flow of more material on either side of the grid, thereby providing a more secure interlock. Although this display is fully functional, it is quite thick, about 0.240xe2x80x3 (appx. 6 mm), making the display somewhat costly to manufacture, and somewhat difficult to manipulate in certain applications (for example, in an application in which slight bending of the display is desired, as in the case of a tag on a utility pole). The manufacturing process is also somewhat involved, since it employs a three-layered first member with a universal grid and spacer system. It was considered important that the grid include spacers at every possible node of the intermediate grid, to ensure that the top surface of the indicia presses evenly against the face of the mold in which the first member is placed during the second shot, to prevent xe2x80x9cflashingxe2x80x9d or leakage of plastic of the second shot over the top of the first member.
There is thus a need in the art for a still further improvement in the field of interlocking plastic display signs, permitting thinner profile displays having improved interlocking and manipulability, and which are easier to manufacture.
It is an object of the invention to provide an interlocking plastic display having a reduced thickness compared to prior art interlocking plastic displays.
In accordance with a preferred embodiment of the invention, an interlocking plastic display has a first member formed as a first shot of an injection molding process. The first member has a top layer which includes a submerged grid system. The grid system is formed only where necessary to connect otherwise unconnected portions of the top layer or to stabilize the top layer where openings may be relatively large. An array of spacers is formed beneath those portions of the top layer having material therein, to space the top layer from the bottom of the mold. No spacers are formed beneath completely open spaces of the top layer. The arrangement of the spacers provides an open area underneath the top layer, so that the second member may be formed in a second injection molding shot and allows the second shot material to flow around and between the spacers on the bottom of the mold. The top of the top layer contacts one side of the mold during the second shot, and the bottoms of the spacers contact the bottom of the mold, so that the first member is maintained in place during the second shot, and thereby prevents slippage of the first member during the second shot. This avoids flashing.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.